Chinese mitten crabs, first reported in the Chesapeake Bay, are more widespread than initially thought. Four crabs have now been caught in Delaware Bay during the last week of May 2007 and may occur in other waters of the U.S. east coast.

In total, seven adult male mitten crabs have been documented from the two bays since 2005. Prior to this, the potentially invasive species had never been recorded from coastal waters of the eastern United States.

The mitten crab is native to eastern Asia and has already invaded Europe and the western United States, where it has established reproductive populations. The crab occurs in both freshwater and saltwater. Young crabs spend their lives in freshwater and migrate to saltwater estuaries for reproduction.

Named for the unusual thick fur-like coating on its claws, the mitten crab looks very different than native crabs and is easily recognized. It is listed as injurious wildlife under the Federal Lacey Act, due to its potential to cause ecological and economic damage.

“We don’t know the present status of this crab along the eastern U.S. coast” says Gregory Ruiz, senior scientist at the Smithsonian Environmental Research Center. “At the moment, it is not clear whether these crabs are reproducing or established in the mid-Atlantic region, or whether the captured crabs are just a few individuals that originated elsewhere” says Ruiz. These crabs may have arrived in the ballast water of ships or through live trade.

A Mitten Crab Network has been established to examine the abundance, distribution, and reproductive status of crabs in Chesapeake Bay, Delaware Bay, and other estuaries along the eastern United States. The initial partnership, between the Smithsonian lab, Maryland Department of Natural Resources, U.S. Fish and Wildlife Service, National Oceanic and Atmospheric Administration, and Delaware Division of Fish and Wildlife, is now being expanded to include resource managers, commercial fishermen, research organizations, and citizens along the east coast.

Anyone seeing a mitten crab is asked to take a close-up photograph if possible and please report it directly to the Mitten Crab Network (443-482-2222; SERCMittenCrab@si.edu ) or a state resource manager.

For more information about the Mitten Crab please see the following links:

First records of Eriocheir sinensis H. Milne Edwards, 1853 (Crustacea, Brachyura: Varunidae) for Chesapeake Bay and the mid-Alantic coast of North America. See the research article published in the journal Aquatic Invasions on the Mitten Crabs found in the Chesapeake Bay.